1. Field of the Invention
The invention relates generally to a mounting arm for hard disk drives. More particularly, the invention relates to a mounting arm for hard disk drives with striations for counteracting residual stress, and method for making the same.
2. Description of Related Art
A key component of any computer system is a device to store data. One common place for storing massive amounts of data in a computer system is on a hard disk drive (HDD). The most basic parts of a disc drive are a disc that is rotated, a mounting arm, such as an actuator arm, that moves a transducer to various locations on the disc, and electrical circuitry that is used to write and read data to and from the disc. There are a variety of disc drives in use today, such as hard disc drives, zip drives, floppy disc drives. All utilize either rotary or linear mounting arms.
In hard disk drives, magnetic heads read and write data on the surfaces of rotating disks that are co-axially mounted on a spindle motor. The magnetically-written “bits” of information are laid out in concentric circular “tracks” on the surfaces of the disks. The disks must rotate quickly so that the computer user does not have to wait long for a desired bit of information on the disk surface to translate to a position under the head. In modern disk drives, data bits and tracks must be extremely narrow and closely spaced to achieve a high density of information per unit area of the disk surface.
The required small size and close spacing of information bits on the disk surface have consequences on the design of the disk drive device and its mechanical components. Among the most important consequences is that the magnetic transducer on the head must operate in extremely close proximity to the magnetic surface of the disk. Because there is relative motion between the disk surface and the magnetic head due to the disk rotation and head actuation, continuous contact between the head and disk can lead to tribological failure of the interface. Such tribological failure, known colloquially as a “head crash,” can damage the disk and head, and usually cause data loss. Therefore, the magnetic head is designed to be hydrodynamically supported by an extremely thin air bearing so that its magnetic transducer can operate in close proximity to the disk while physical contact between the head and the disk is minimized or avoided. Typically, the head-to-disk spacing present during operation of modern hard disk drives is extremely small, measuring in the tens of nanometers.
The mounting arm is typically used to move a magnetic transducer in close proximity to a disc. It must be of a sufficiently high stiffness to withstand acceleration forces, vibration and mechanical shock occurring during operation of a disk drive. FIG. 1 illustrates a prior art mounting arm 10. The mounting arm 10 comprises a generally planar region 11 with an opening 12 for insertion of a pivot bearing cartridge. It has a cantilevered section 13 that couples, via a boss hole 14, to at least one suspension arm (not shown) at the distal end via laser welding. Attached to the suspension are recording heads/sliders which include magnetic transducers that magnetize the surface of the disk (not shown). The mounting arm 10 may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down. Typically, the mounting arm 10 has a length 20 of about 1.4 inches, a width 16 of about 0.20 inches, and a thickness of about 0.012 inches. The mounting arm 10 may be made from 300 Series stainless steel material, for example.
Characteristics of the mounting arm used for moving the magnetic transducer in close proximity to the disk must be considered by the designer to minimize vibration in response to rapid angular motions and other excitations. For example, the mounting arm must be stiff enough and the mounting pivot bearing must be of high enough quality so that the position of the head can be precisely controlled during operation. Also, the interface between the mounting arm and the pivot bearing must be of sufficient rigidity and strength to enable precise control of the head position during operation and to provide the boundary conditions necessary to facilitate higher natural resonant frequencies of vibration of the mounting arm. The stiffness of the mounting arm must also be sufficient to limit deflection that might cause contact with the disk during mechanical shock events.
The mounting arm is typically made from full hard 300 series stainless steel strip. The stainless steel is tension leveled to relieve any abnormalities in the residual stress within the material resulting in a state optimized for flat stamping. Regardless of the incoming stress state, the effect of cutting an irregular periphery from the raw material is one that yields a characteristic shape that is rarely the desired shape. Consequently, die forming is employed to counteract the post-edge cut shape and add any desired shape.
To force full hard stainless steel to take a desired shape, over-bending is required. This over-bending requires shaped tooling that is difficult to manufacture, expensive and only applicable to a given raw material lot. Once the incoming material changes, the required punch shape will be different to compensate for the changes. This requires frequent tooling changes, which is cost prohibitive.
Most state-of-the-art fabrication attempts to improve the incoming residual stress condition of the raw material have had limited short term success. Conventional EDM shaped punches that are typically used in the industry have limited short term success. Optimizing cutting clearances to minimize distortion through stamping has also been attempted. Matching punch shapes of a presumed best shape have also been tried. All these fabrication methods fail to achieve the result of shifting the shape of the mounting arm with small variation or have the ability to adjust the fabrication method quickly and easily.
Therefore, there is a need in the art for a mounting arm with improved residual stress condition by providing localized compressive stress zones, easily applied to the mounting arm, to adjust the shape of the mounting arm.